Amendment of Sargassum oligocystum bio-char with MnFeO and lanthanum MOF obtained from PET waste for fluoride removal: A comparative study.

The use of biomass and waste to produce adsorbent reduces the cost of water treatment. The bio-char of Sargassum oligocystum (BCSO) was modified with MnFeO magnetic particles and La-metal organic framework (MOF) to generate an efficient adsorbent (BCSO/MnFeO@La-MOF) for fluoride ions (F) removal from aqueous solutions. The performance of BCSO/MnFeO@La-MOF was compared with BCSO/MnFeO and BCSO. The characteristics of the adsorbents were investigated using various techniques, which revealed that the magnetic composites were well-synthesized and exhibited superparamagnetic properties. The maximum adsorption efficiencies (BCSO: 97.84%, BCSO/MnFeO: 97.85%, and BCSO/MnFeO@La-MOF: 99.36%) were achieved under specific conditions of pH 4, F concentration of 10 mg/L, and adsorbent dosage of 3, 1.5, and 1 g/L for BCSO, BCSO/MnFeO, and BCSO/MnFeO@La-MOF, respectively. The results demonstrated that the experimental data adheres to a pseudo-second-order kinetic model. The enthalpy, entropy, and Gibbs free energy were determined to be negative; thus, the F adsorption was exothermic and spontaneous in the range of 25-50 °C. The equilibrium data of the process exhibited conformity with the Langmuir model. The maximum adsorption capacities of F ions were determined as 10.267 mg/g for BCSO, 14.903 mg/g for the BCSO/MnFeO, and 31.948 mg/g for BCSO/MnFeO@La-MOF. The K and A values for the F adsorption were obtained at 21.03 mg/g (L/mg) and 100 × 10 L/g, indicating the pronounced affinity of the BCSO/MnFeO@La-MOF towards F than other samples. The significant potential of the BCSO/MnFeO@La-MOF magnetic composite for F removal from industrial wastewater, makes it suitable for repeated utilization in the adsorption process.